A distinct pattern of inflammatory lesions, consisting of focal non-suppurative necrotizing encephalitis, non-suppurative myocarditis and myositis have been observed in many aborted bovine fetuses submitted for diagnosis. The pattern of lesions, particularly in the brain, is similar to those seen with Toxoplasma gondii infections in sheep. However, cattle have been reported to be resistant to T. gondii infection (Dubey, Vet. Parasit. 22:177–202 (1986)). In 1988, a cyst-forming protozoal parasite was first identified by histopathological examination in fetuses (Barr, et al., Vet. Parasit. 27:354–61 (1990)). This parasite was morphologically similar to Toxoplasma, except that some of the cysts had thick walls, which was more similar to the Neospora caninum-like protozoan observed by Thilsted & Dubey (J. Vet. Diagnos. Invest. 1:205–9 (1989)) in aborted fetuses from a dairy in New Mexico.
Further studies showed the protozoal parasites associated with inflammatory lesions in aborted fetuses and neonatal calves in California had ultrastructural and antigenic features that were most similar to N. caninum parasites which were originally isolated from dogs (Dubey, et al., JAVMA 193:1259–63 (1988)). However, differences in the antigenic reactivity of the bovine protozoan and N. caninum when tested with a panel of antisera indicated they might not be from the same species (Barr, et al., Vet. Pathol. 28:110–16 (1991)).
A more complete understanding of the identity and biology of these bovine protozoa requires establishing continuous in vitro cultures of the parasites. Such cultures would also be valuable in the development of diagnostic assays and pharmaceutical compositions for the treatment and prevention of Neospora infections. The present invention addresses these and other needs.